Conventional pillow cores have been made of materials such as silk cotton, feathers or the like. When the user rests his or her head on a pillow having such a core, the pillow tends to sink at the associated portion thereof because of the inadequate supporting capacity of its core. As a result, users may not feel well when their body turns over. Besides, a pillow made of such materials will become contaminated if frequently used, even if a pillow-towel or pillow case is used to cover it. A pillow may also acquire an offensive odor if stored for a long period of time. Moreover, it can be troublesome to wash and dry a pillow with silk cotton or feathers within it.